Defending champion Victoria Azarenka, Maria Sharpova and Caroline Wozniacki have all reached the second round of the Australian Open.

Temperatures soared above 40C but that was still not enough for the tournament to implement the extreme heat policy, which would see play suspended on open courts and the roof shut on Rod Laver and Hisense Arena.

Whether the policy is used is a decision made by tournament referee Wayne McKewen, and a combination of heat and humidity is taken into account.

Second seed Azarenka, who has won the title for the last two years, spent an hour and 46 minutes on court in defeating Swede Johanna Larsson 7-6 (7/2) 6-2.

Larsson twice served for the first set only for Azarenka to break back and then win the tie-break convincingly.

The Belarusian described the conditions as "like dancing in a frying pan", but said: "It wasn't too bad. I went to practise after so I'm okay.

"It's not easy those conditions but it's the same for everybody. You just have to adapt to it and try to do the best things to prepare. Actually I felt better as the match was going on than in the beginning."

"I put a (drink) bottle down on the court and it started melting" - Caroline Wozniacki

Azarenka, who meets Czech Barbora Zahlavova Strycova in the next round, was not concerned by her first-set struggles.

She said: "She played really well. I can't say that I was surprised by that. She really went for her shots. The ball bounced a lot higher, which suited her. It took me a little bit of time to find my range."

There was a scare for eighth seed Jelena Jankovic when she fell during her match against Japan's Misaki Doi and needed treatment to her ankle, but she recovered to win 6-1 6-2.

Eleventh seed Simona Halep, who won more titles than any other woman except Serena Williams last season, was an even more emphatic winner, the Romanian defeating qualifier Katarzyna Piter 6-0 6-1.

Sharapova battled her way to victory over America's Bethanie Mattek-Sands.

The 6-3 6-4 scoreline did not really do justice to how hard Sharapova was made to work in the 99 minutes the pair spent on court.

Mattek-Sands, who as usual stood out from the crowd with her purple hair and knee-length black socks, was a tough draw for the third seed and she scrapped all the way to the finish.

Sharapova was playing her first grand slam match since Wimbledon, having missed the US Open with shoulder problems that brought an early end to her season.

The Russian was straight back into the groove, moving into a 4-0 lead despite Mattek-Sands having her chances.

The American stopped the rot with two straight games, but Sharapova held on to her advantage to take the set.

Mattek-Sands fought back in the second set as well to lead 4-3, having trailed 3-1, but Sharapova always looked to have enough to win the games that mattered, and so it proved.

The world number three goes through to face Italy's Karin Knapp, who defeated Paula Ormaechea of Argentina.

Wozniacki said of the conditions: "It was a little warm out there today. I put a (drink) bottle down on the court and it started melting a little bit underneath. It was great that I managed to finish it off in two sets and it wasn't too long."

Wozniacki is playing in her first grand slam since becoming engaged to golfer Rory McIlroy but insists she is as hungry as ever to try to be a grand slam force once more.

The 23-year-old has not reached the quarter-finals at one of the sport's four biggest tournaments for two years.

She added: "I think I'm in a very good place in my life right now, on the court and off the court. I know what I want. I want to improve all the time. I want to be the best."